Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2002-08-23
2004-07-13
Stephens, Juanita D. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S009000
Reexamination Certificate
active
06761423
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an ink-jet printing apparatus, and more particularly, to an improved ink jet printing apparatus that can effectively prevent the viscosity of the ink filled in the ejecting nozzles from increasing and reduce ink jam at the ejecting nozzles.
2. Description of the Related Art
Recently, ink-jet printers that are usable as an output apparatus of an information processing apparatus (e.g., computers) have attracted a lot of attention. With an ink-jet printer, the running cost is less, while highly precise imaging and coloring processes are realized with a relatively simple technique. However, there are still many points to be improved in the ink-jet recording head of ink-jet printers.
The ink-jet head of an ink jet printer has a plurality of nozzles and pressure chambers communicating with the openings of the respective nozzles. An ejection energy generating means is driven in response to a print command to change the pressure in the chamber, which causes the ink to be ejected from the nozzles.
Ink droplets attached onto a recording medium may blur depending on the quality of the recording medium (e.g., paper quality), or may undesirably come into contact with other members and be smeared. To avoid such situations, ink is generally prepared so that the solvent promptly permeates the recording medium and then evaporates to fix the ink on the recording medium. However, this causes another problem, that is, the viscosity of ink increases due to evaporation of the solvent, especially in those nozzles that are not frequently used. The same problem also occurs it the printing operation is suspended for a while. Increase in ink viscosity causes ink jam. This problems becomes conspicuous when using an aqueous (water) ink containing a high-viscosity organic solvent, such as a humectant, containing as main components water and glycol or similar material. To prevent this problem, the nozzle openings are capped when the printing operation is suspended for a relatively long time, thereby preventing the evaporation of the ink solvent.
However, this countermeasure cannon prevent the ink jam from occurring during the printing operation in general, ink ejection is not uniform at all the nozzles, and there are some nozzles whose ejection frequency is quite low or which do not eject ink tar a long time, depending on the positional arrangement of the nozzle openings or on print data. At these nozzles, the ink solvent evaporates, and the viscosity of the ink filled in the nozzles increase. This results in the ink ejecting condition changing, and the dot positions are offset from the correct positions on the recording medium. In addition, ink ejection becomes unstable, and dots deform or are lacking. In the worst case, ink can not be ejected from the nozzles due to ink jam.
To overcome this problem, a technique for refreshing the ink in the nozzle to return the ink condition to the initial state has been proposed. This technique is used in a serial type printer in which the ink head moves with respect to the recording medium to print. With this technique, the recording head recedes to the non-printing area (i.e., the return area for the to-and-fro motion) after it carried out the printing operation for a predetermined time. In the non-printing area, a prescribed number of ink droplets are forcibly ejected from all the nozzle openings (which is referred to as spraying) to refresh the ink in the nozzle, and thereby returning to the initial condition.
However, this technique has several drawbacks. First, the printing operation has to be stopped regularly, and the printing rate is reduced. In addition, since in recent years the quantity of an ink droplet forming a dot is as little as several pico liters (pL), the interval between the spraying must be shortened to prevent the viscosity of the ink from increasing. This further causes the printing rate to decrease. Furthermore, the spray operation causes the ink consumption to increase. In order to conduct the spraying in a line printer in which a recording medium moves with respect to the recording head, an extra space for carrying out the spraying is needed, and the entire apparatus becomes large.
In conclusion, spraying cannot entirely solve the problems associated with increase of the ink viscosity.
There are some other known techniques for preventing ink jam. For example, Japanese Patent Application Laid-open (Kokai) No. 55-123476 discloses a printing apparatus using piezoelectric elements as ink-ejection energy generating means. In this apparatus, during the printing operation, a printing signal is applied, via a current-control resistance, to the piezoelectric element in the pressure chamber that corresponds to the nozzle not ejecting the ink, thereby slightly vibrating the liquid surface in the nozzle.
Japanese Patent Publication-after-Examination (Kokoku) No. 62-33074 and Japanese Patent Application Laid-open No. 4-80037 also disclose a technique for preventing ink jam by applying a voltage to the piezoelectric elements so as not to eject a ink droplet, but to vibrate the liquid surface at the nozzle openings. With this technique, it is not necessary for the apparatus to stop the printing operation, and therefore, the printing rate can be maintained, while preventing unnecessary ink consumption.
Slightly vibrating the liquid surface of the ink causes the ink particles to diffuse in the nozzle, thereby preventing the viscosity from increasing. This method is effective when using ink whose viscosity changes only gently and when the non-ejecting time is relatively short. If the non-ejecting time is long, the increase in viscosity can be still prevented by combining the liquid-surface vibrating method with the spraying technique.
However, in order to slightly vibrate the ink surface in the nozzle, a voltage is always applied to the ink ejecting means including during the non-printing period. This leads to still another problem in that the ink-ejection energy generating means wears easily, and the service life is shortened.
SUMMARY OF THE INVENTION
The present invention was conceived in view of the above-described problems, and it is an object of the present invention to provide an ink-jet printing apparatus that can produce slight vibration on the liquid surface in the nozzle in a efficient manner, while reducing the number of times of driving the ink-ejection energy generators. To achieve this object the ink-jet printing apparatus according to the present invention makes positive use of a so-called crosstalk phenomenon, in which the liquid surface of ink at a nozzle opening slightly vibrates under the influence of ink ejection from the adjacent nozzles.
In one aspect of the invention, an ink-jet printing apparatus comprises a plurality of nozzles configured to eject ink; pressure chambers, each corresponding to one of the nozzles; ink-ejection energy generators, each being provided to one of the pressure chambers; and a vibration controller configured to apply a non-ejecting vibration signal to the ink-ejection energy generator to cause the liquid surface of ink filled in the associated nozzle to slightly vibrate. The nozzles are grouped into two or more groups, and the vibration controller supplies the non-ejecting vibration signal to the ink-ejection energy generators of each nozzle group at a different timing. The voltage of the non-ejecting vibration signal is regulated so as not to cause the ink to eject from the nozzle, but only to slightly vibrate at the opening of each nozzle.
In other words, the vibration controller drives and causes the ink-ejection energy generator no produce energy that does not eject the ink from the nozzle, but causes the ink surface to slightly vibrate at the nozzle opening. The non-ejecting vibration signal is supplied sequentially to each nozzle group, varying the signal supply timing for each group. With this arrangement, the ink surface at a nozzle opening is always slightly vibrating, even when the non-ejecting vibration s
Ozaki Mitsuo
Suzuki Shigeharu
Tokuyo Shino
Armstrong Kratz Quintos Hanson & Brooks, LLP
Fuji Photo Film Co., LTD
Stephens Juanita D.
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